1. Field of the Invention
The present invention relates to methods and apparatus for depositing a layer on a localized area on a substrate. The invention has particular, although not exclusive application for use in a metrology method for use in a lithographic method for manufacturing a device.
2. Background Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (photo resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In order to monitor the lithography process it is necessary to measure the dimensions of topographical features present on a substrate, which has been processed in the lithographic apparatus, for example the width of lines of a pattern formed on the photo resist by the lithography process. This may be performed using a Transmission Electronic Microscope (TEM), in which case it is necessary to deposit an electrically conductive layer over the photo resist.